A. Field of the Invention
The present invention relates to a flywheel assembly, and in particular to a flywheel assembly including two flywheels with a damper mechanism disposed therebetween.
B. Description of the Background Art
A flywheel is attached to an end of a crankshaft of an engine for preventing variation in rotational speed during a low-speed driving by providing a mass or a moment of inertia. A ring gear for a starter, a clutch mechanism typically are fixed to the flywheel.
One flywheel assembly is formed with a divided flywheel where there are first and second flywheels and a damper mechanism disposed between them. The damper mechanism includes elastic members which are compressed in a circumferential direction of the flywheel assembly when the flywheels rotate relative to each other. The damper mechanism may employ a slider mechanism which operates in a parallel with the elastic members.
A driving system of a vehicle causes noises and vibrations such as gear noises and internal resonance noises during driving. In order to reduce these noises and vibrations, it is necessary to lower the torsional rigidity in an acceleration and deceleration torque range and thereby lower a torsional resonance frequency of the driving system below a service rotation range. In order to lower the torsional rigidity of the damper mechanism, a maximum torsion angle of elastic members may be increased, and/or a plurality of elastic members may be arranged to operate in series.
In a flywheel assembly where two flywheels are employed, the rotation changes through a resonance point at a low rotation range, e.g., lower than 500 rpm during start and stop of the engine. During these operations, an excessive torque variation is generated, which results in breakage of the damper mechanism and/or large noises and vibrations in some cases. For overcoming these problems, a flywheel assembly is known that employs a frictional coupling mechanism arranged for transmitting torque in series with an elastic coupling member, for example, as disclosed in Japanese Patent Publication No. 7-92114 (92114/1995). In the flywheel assembly, when an excessive torque variation occurs during change of the rotation through a resonance point in a low rotation range (e.g., lower than 500 rpm), a slide occurs on a friction member of a frictional coupling mechanism and thereby a large hysteresis torque is produced, by which the vibration is damped. Therefore, noises and vibrations at the time of resonance can be suppressed.
In this flywheel assembly of Japanese Patent Publication No. 7-92114 (92114/1995), however, the frictional coupling mechanism is disposed radially inside the elastic coupling member. Therefore, the friction member has a small radius, and therefore it is difficult to generate a large hysteresis torque. A large pressing load must be applied by a biasing member in order to generate a large hysteresis torque. This causes instability in magnitude of the hysteresis torque.